In the past decade, signal and data processing aboard spacecrafts have advanced rapidly from KIPS or kilo instructions per second to MIPS or millions of instructions per second. The result is the utilization of increasingly powerful commercial technology which has to be adapted for space applications.
However, as is common in the design of electronics carried in space vehicles, a massive amount of redundancy has heretofore been utilized such that if one of the particular processing systems goes down due to massive incoming radiation or due to component failures, it was the policy to provide for redundant processing to repair the electronics by simply duplicating it and calling up the duplicate processor.
However, with increased processing loads the amount of a weight and space occupied by such redundant systems has become excessive. Additionally, the utilization of redundant systems requires increased power resources which are unavailable at the spacecraft. Thus there is a limit of how much redundancy one can achieve given the limited space and power resources available on, for instance, a communications satellite.
Moreover, due to the long time span of missions lasting from several years to over decades, the applications for the processing elements for the spacecraft sometimes needs to be changed due to different requirements that did not exist at the time of launch. This means that there is a requirement to be able to flexibly change the signal processing capabilities of the on-board electronics package and to do so not only to accommodate system element failure, but also to accommodate new mission objectives.
In the early days of space flight in the United States, triple redundancy was thought to be sufficient to counteract system failures during the relatively short space flights involved. For instance, in manned programs, the missions were at most a number of weeks as opposed to number of decades. Thus for manned space flight, triple redundancy was sufficient due to the relatively short duration of the space flight.
However, for longer missions involving multiple years to decades, not only was it necessary to be able to accommodate subsystem failures, it was necessary to be able to repair the downed subsystems without costly individual element redundancy. For mission changes individual element redundancy was likewise inappropriate.
Thus, with decade long missions, and with power at a premium, to say nothing of payload weight, there is a requirement for providing a fundamentally different methodology for accommodating system failure and mission changes.